Engines in hybrid vehicles may operate for shorter durations enabling fuel economy and reduced fuel emissions. However, these shorter engine operation times can lead to fuel residing in a fuel tank for longer intervals. Further, a vehicle operator may refuel the fuel tank even though the fuel tank contains residual fuel. For example, vehicle operators may fill the fuel tanks in spite of considerable residual fuel when fuel prices are lower, when a favored filling station is nearby, or prior to a long trip. Thus, the fuel tank may contain different fuels after a refueling event. Specifically, residual fuel (prior to refueling) in the fuel tank may have a distinct octane rating, a distinct ethanol content, or a different volatility relative to new fuel received during the refueling event. If the hybrid vehicle is operated in an engine-off mode following the refueling event, residual fuel and fuel received during refueling may remain substantially unmixed. Furthermore, engine operation at a later time may be adversely affected by fueling errors due to non-uniformity of the fuel. For example, an ethanol estimation routine that is activated when engine operation is commenced may produce distorted results causing errors in fuel injection and air/fuel ratio. As such, fueling errors can produce combustion instabilities and reduce engine performance.
The inventor herein has recognized the above issues and identified an approach to at least partly address the issues. In one example approach, a method for a hybrid vehicle is provided, comprising responsive to a refueling event with an amount of residual fuel in a fuel tank higher than a threshold fill, activating a fuel pump located within the fuel tank without injecting any fuel to the engine. In this way, residual fuel and newly received fuel may be blended in the fuel tank.
As one example, a hybrid vehicle may be propelled by one or more of an engine and a motor. When the engine is activated and combusting, the engine may receive fuel from a fuel tank coupled in the hybrid vehicle. Specifically, an electrically actuated fuel pump may supply fuel from the fuel tank to the engine. If an operator of the vehicle initiates a refueling event even though the fuel tank contains fuel with a fill level that is higher than a threshold, the fuel pump may be actuated to promote mixing of residual fuel with fresh fuel. In one example, the fuel pump may be activated during the refueling event. In another example, the fuel pump may be activated immediately following the refueling event if the hybrid vehicle begins operating in an engine-off mode (e.g., when the engine is shut down to rest). As such, the fuel pump may be activated during (or subsequent to) the refueling event without operating the engine.
In this way, a fuel tank may comprise fuel of a more uniform composition subsequent to refueling with a substantial amount of residual fuel in the fuel tank. Fresh fuel entering the fuel tank may be mixed with residual fuel existing in the fuel tank (prior to refueling) by activating the fuel pump in response to the refueling event. The technical effect of ensuring that fuel in the fuel tank has a more uniform composition is that fueling errors may be reduced and a desired air/fuel ratio may be achieved during engine operation. Since the fuel pump is activated without operating the engine, fuel economy may be maintained. Overall, a desired engine performance may be realized.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.